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ASTM C748-98(2005)

(Test Method)

Standard Test Method for Rockwell Hardness of Graphite Materials

Standard Test Method for Rockwell Hardness of Graphite Materials

SIGNIFICANCE AND USE
A Rockwell L scale hardness number is a number derived from the net increase in depth of impression as the load on a 6.3500- ± 0.0025-mm (0.2500- ± 0.0001-in.) diameter steel-ball indenter is increased from a fixed 10-kg minor load to a 60-kg major load and then returned to the minor load.  
A Rockwell hardness number is directly related to the indentation hardness of a material; the higher the Rockwell L scale reading, the harder the material. The test is useful in the evaluation and the manufacturing control of carbon and graphite materials.
SCOPE
1.1 This test method covers Rockwell L scale hardness testing of graphite materials with grain size less than 0.8 m (0.032 in.) and a hardness range between 0 and 120.
1.2 Test Methods E 18 shall be followed except where otherwise indicated.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are provided for information purposes only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

Status
Historical
Publication Date
30-Apr-2005
ICS
71.060.10 - Chemical elements
Technical Committee
D02 - Petroleum Products, Liquid Fuels, and Lubricants
Drafting Committee
D02.F0 - Manufactured Carbon and Graphite Products
Current Stage
Ref Project

Relations

Replaces
ASTM C748-98 - Standard Test Method for Rockwell Hardness of Graphite Materials
Effective Date
01-May-2005
Replaced By
ASTM C748-98(2010)e1 - Standard Test Method for Rockwell Hardness of Graphite Materials
Effective Date
01-May-2010
Referred By
ASTM D7775-21 - Standard Guide for Measurements on Small Graphite Specimens
Effective Date
01-May-2005

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ASTM C748-98(2005) - Standard Test Method for Rockwell Hardness of Graphite MaterialsASTM C748-98(2005) - Standard Test Method for Rockwell Hardness of Graphite Materials
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ASTM C748-98(2005) - Standard Test Method for Rockwell Hardness of Graphite Materials
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
An American National Standard
Designation:C748–98 (Reapproved 2005)
Standard Test Method for
Rockwell Hardness of Graphite Materials
This standard is issued under the fixed designation C748; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope scale reading, the harder the material. The test is useful in the
evaluation and the manufacturing control of carbon and graph-
1.1 This test method covers Rockwell L scale hardness
ite materials.
testing of graphite materials with grain size less than 0.8 m
(0.032 in.) and a hardness range between 0 and 120.
5. Apparatus
1.2 Test Methods E18 shall be followed except where
5.1 RockwellHardnessTester,calibratedinaccordancewith
otherwise indicated.
the requirements of Section 7.
1.3 The values stated in SI units are to be regarded as the
5.2 Rockwell Hardness Tester Anvil, appropriate for the
standard. The values given in parentheses are provided for
material shall be used as the specimen base plate.
information purposes only.
1.4 This standard does not purport to address all of the
6. Test Specimen
safety concerns, if any, associated with its use. It is the
6.1 The recommended test specimen shall be flat and have a
responsibility of the user of this standard to establish appro-
minimum thickness of 6.35 mm ( ⁄4 in.).
priate safety and health practices and determine the applica-
6.2 The test surface roughness shall not exceed 3175-nm
bility of regulatory limitations prior to use.
(125-µin.) arithmetical average.
2. Referenced Documents 6.3 The test surface to opposite face parallelism for flat
2 specimens shall be within 1 %. For all other specimen shapes,
2.1 ASTM Standards:
the test surface must be maintained normal to the direction of
E18 Test Methods for Rockwell Hardness of Metallic Ma-
load application.
terials
E171 Specification for Atmospheres for Conditioning and
7. Verification of Calibration
Testing Flexible Barrier Materials
7.1 Level the Rockwell hardness tester in accordance with
3. Summary of Test Method the manufacturer’s instructions.
7.2 The adjustment of speed-of-load application is of great
3.1 The specimen is held in position and the load is applied.
importance. Adjust the dashpot on the Rockwell tester so that
Final position of the indicator on the scale is observed and
the operating handle completes its travel in 4 to 7 s with no
recorded as the hardness number.
specimen on the machine or no load applied by the indenter to
4. Significance and Use the anvil. The major load shall be 60 kg for this calibration.
When so adjusted, the period taken for the mechanism to come
4.1 A Rockwell L scale hardness number is a number
to a stop with the specimen in place will vary from 5 to 15 s,
derivedfromthenetincreaseindepthofimpressionastheload
depending upon the particular specimen, the indenter, and the
on a 6.3500- 6 0.0025-mm (0.2500- 6 0.0001-in.) diameter
load used. The operator should check the instrument manual
steel-ball indenter is increased from a fixed 10-kg minor load
for this adjustment.
to a 60-kg major load and then returned to the minor load.
7.3 Select a test block for Rockwell L scale ball-type
4.2 A Rockwell hardness number is directly related to the
indenters and make five impressions on the test surface of the
indentation hardness of a material; the higher the Rockwell L
block. Compare the average of these five tests against the
hardness calibration of the block. If the error is more than 62
This test method is under the jurisdiction of ASTM Committee D02 on
hardness numbers, the machine or penetrator, or both, must be
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
checked to determine and correct the cause of error.
D02.F0 on Manufactured Carbon and Graphite Products.
Current edition approved May 1, 2005. Published May 2005. Originally
8. Conditioning
approved in 1973. Last previous edition approved in 1998 as C748 – 98. DOI:
10.1520/C0748-98R05.
8.1 Allow the specimen(s) to reach equilibrium with room-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
temperature air, and test under the same conditions in accor-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
dance with Specification E171.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C748–98 (2005)
8.2 Keep specimens free from contamination. vicinity of other machines, the tester should be effectively
protected. Mounting the hardness tester on a metal plate with
9. Procedure
25-mm (1-in.) thick spo
...

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5.1 The Molten Salt Reactor is a nuclear reactor which uses graphite as reflector and structural material, and molten salt as coolant. The graphite components will be submerged in the molten salt during the lifetime of the reactor. The porous structure of graphite may lead to molten salt permeation, which can affect the thermal and mechanical properties of graphite. Consequently, it may be necessary to measure the various strengths of the manufactured graphite materials after impregnation with molten salt and before exposure to the reactor environment in a range of test configurations in order for designers or operators to assess their performance.
Note 1: Depending upon the salt selected for the reactor, there may be some chemical reaction between the salt and the graphite that could affect properties. The user should establish, prior to following this guide, that any interactions between the molten salt and graphite are understood and any implications for the validity of the strength tests have been assessed.  
5.2 For gas-cooled reactors, the strength of a graphite specimen is usually measured at room temperature. However, for molten salt reactors, the operating temperature of the reactor must be higher than the melting temperature of the salt, and so the salt will be in solid state at room temperature. Consequently, room temperature measurements may not be representative of the performance of the material at its true operating conditions. It is therefore necessary to measure the strength at an elevated temperature where the salt is in liquid form.
Note 2: Users should be aware that a small increase in graphite strength is expected with increasing temperature. Testing at the plant operating temperature will eliminate this small uncertainty.  
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5.4 For the test results to be meaningful, the...
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Standard Guide for Impregnation of Graphite with Molten Salt

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5.1 The molten salt reactor is a nuclear reactor which uses graphite as reflector and structural material and fluoride molten salt as coolant. The graphite components will be submerged in the molten salt during the lifetime of the reactor. The porous structure of graphite may lead to molten salt permeation, which can affect the thermal and mechanical properties of graphite. Consequently, it is important to assess the effect of impregnation of molten salt on the properties of the as-manufactured graphite material.  
5.2 The purpose of this guide is to report considerations that should be included in the preparation of graphite specimens representative of that after exposure to a molten salt environment. The degree to which the molten salt will infiltrate the graphite will depend upon a number of factors, including the type of graphite and the type and extent of porosity, the properties of the molten salt, the impregnation pressure and temperature, and the duration of the exposure of the graphite to the molten salt.  
5.3 The user of this guide will need to select impregnation parameters sufficiently representative of those in a molten salt reactor based on parameters provided by the designer. Alternatively, the user may select a standard set of impregnation conditions to allow comparisons across a range of graphites.  
5.4 This guide is not intended to be prescriptive. A typical apparatus and associated procedure are described. Some indication of the sensitivity of the procedure to graphite type and impregnation conditions is given in He, et al.5  
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5.5.1 The density of molten salt is greater than that of graphite. A specially designed tool is required to submerge graphite samples in the molten salt during the impregnation process.  
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4.1 Carbon and graphite can usually support higher loads in compression than in any other mode of stress. This test, therefore, provides a measure of the maximum load-bearing capability of carbon and graphite objects.
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1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
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